This invention relates to improved methods and apparatus for obtaining well-logging information, and more particularly relates to improved methods and apparatus for efficiently transforming digital well logging information into a more useful and informative format.
It is conventional practice in the search for petroleum substances residing in subsurface earth formations to drill boreholes into such formations, and to survey the earth materials along the length of the boreholes to determine possible locations therein where oil or gas may be recovered. These boreholes are normally surveyed or "logged" by passing a "sonde" through the borehole which contains devices capable of measuring various lithological parameters of interest, and thereafter recovering these measurements on the surface for analysis.
In the early history of well logging, logging measurements were relatively simple and severely limited by factors such as equipment and the like. Moreover, log data analysis techniques were somewhat unsophisticated and data processing limitations were accordingly not of particular significance. However, as the art of well logging progressed, measurements and log analysis techniques have become far more complex, such that massive amounts of logging information are being generated and in relatively short periods of time, and often require analysis and processing in correlatively small time periods. For example, a well logging system of the type depicted and described in the aforesaid U.S. patent application Ser. No. 949,592, has been developed for simultaneously generating and transmitting to the surface complex measurements from a plurality of logging tools. Moreover, not only has the number of parameters being simultaneously measured increased, but as previously noted the rate at which these measurements are available for processing has increased tremendously. This may be due to a number of factors, including the faster rate at which the sonde is now caused to traverse the borehole and thus generate measurements, the increasingly smaller increments of borehole which must be sampled, and the statistical nature of some of the more modern logging tools.
Still further, demand for more efficient processing of well logging information has not only been created by the increased complexity and arrival rate of information generated from within the borehole, but from other considerations as well. For example, as the science of well log analysis continues to develop, more complex relationships between measured parameters are being discovered, which require attendant increases in processing time to transform these measurements into newly derived functions. Moreover, demands for improved methods for effective visual display of logs so as to be more informative and useful have still further compounded the problem. It has been found desirable, for example, to cause derived measurements to be presented in graphical form on a suitable terminal device, such as a video display of high resolution capability wherein the various measurements must be scaled appropriately, and wherein various additional features such as display of reference grid lines lithological symbols, alpha-numeric messages, and the like, all functionally related to these measurements, may also be displayed. Accordingly, additional time must be devoted to the generation of data related to these functions. The combination of this data with the derived well logging information further compounds the problem of increasing the data transfer rate of well logging information processing systems which have already been taxed to their limits.
One attempted solution to the hereinbefore noted problems caused by the tremendous increase in volume and required rate of processing of information generated in a modern well logging operation is to produce logs at a decreased rate so as to provide additional time for information processing. Due to the tremendous capital investments in equipment and labor costs associated with logging and drilling operations, however, it is highly undesirable to extend the time required to produce measurements so as to permit the processing at slower rates. Yet another attempt to solve the hereinbefore noted problems is to provide for high speed storage of information as it is generated, whereby it may be thereafter retrieved after a log is run and processed at much slower rates. However, even after a log has been made, it is often undesirable to further tie up logging and drilling equipment and labor by decisions regarding the well which must be delayed while the vast amount of information, is being processed, displayed and analyzed.
Still another attempt to alleviate the requirements for more efficient information processing and data transfer rates in modern well logging operations has been to divide the computational tasks which must be performed in the analysis and transformation of logging information between two processors which may be operating simultaneously. For example, it is known that one processor may process data and store results in a first memory while a second processor simultaneously processes different data and stores results in a second memory, after which the two memories may be interchanged so as to enable the second processor to thereafter further process data resulting from the first processor's operations. However, it has been found that attempts to provide for such simultaneous operation of processors creates still further problems and often require two large computers which are unsuitable for remote well site logging operations. For example, it frequently takes more time to coordinate the functions being performed by each controller than is saved by the fact that they are processing information simultaneously. Excessive time is required to interchange memories or to detect when both processors hve completed their tasks and are ready for transfer. Moreover, one processor may have to remain idle until the other processor completes its tasks.
Thus, in summary, it will be seen that due to large quantities of logging information produced at high data rates, it would be desirable to significantly increase the rate at which this data is processed and transferred. This would allow for production of more elaborate and useful information in real time during a logging operation so as to permit enhanced monitoring and adjustment, as well as to decrease the time necessary to provide permanent visible records of the logging operation. It has been seen that a solution to the hereinbefore noted problems must avoid "tying up" a well and associated equipment either during the logging process by slowing down the logging rate or taking multiple passes through the borehole, or after the log has been produced. Thus, it is desirable to minimize the processing time after a log is made as well as during the log, so as to produce logs quickly, provide additional information during the logging process in real time so that portions of the borehole may be relogged or the like if desired, and to permit generation of time consuming visible records of logging data during a logging operation. Moreover, it is also desirable to achieve these results with equipment which is relatively light, compact, and suitable for portable operation in a logging truck at well site.
The disadvantages hereinbefore noted are overcome with the present invention, and novel means and methods are provided for efficiently processing and transferring well logging information. A novel system and method is provided for processing well logging information at high data transfer rates, which not only improves the logging operation and amount of information which may be presented, and eliminates the need to restrict logging rates or occupy wells, equipment, and personnel for unnecessarily long periods, but does so with compact and light apparatus suited to mobile operations.